View Compilation Error

0_0_17389591_2067.cpp:9:11: error: '::main' must return 'int'
 void main(){
           ^
0_0_17389591_2067.cpp: In function 'int main()':
0_0_17389591_2067.cpp:12:25: error: 'strlen' was not declared in this scope
   int lenstr1 = strlen(a);
                         ^